Cut off the woody white ends of the asparagus spears. If desired, remove the tough fibrous outer layer from the lower half of each spear using a vegetable peeler.
In a straight-sided saute pan, heat oil until smoking. Add asparagus in a single layer. Season with salt and pepper and cook undisturbed until lightly browned, 1-2 minutes. Shake pan to turn spears and cook another 1-2 minutes. Add stock and butter to pan and immediately cover.
Cook until spears are tender and butter and stock have emulsified into a lightly-thickened sauce, 7-10 minutes. (If sauce evaporates and butter begins to burn, add a couple of tablespoons of water.) Serve at once.